1. Field of the Invention
The present invention relates to a zoom lens system, and more particularly to a two group zoom lens system in which an air space, formed between the two groups, is varied in a zooming operation.
2. Description of the Prior Art
In this field of art, it is well known to provide a two group zoom lens system which has a first negative lens group at the front of the zoom lens system and a second positive lens group located at the image side of the first lens group with a variable air space formed between the first and second lens groups. In this zoom lens system, the first and second lens groups are shiftable along the optical axis with the variable air space changing during a zooming operation, and the first lens group alone is shiftable along the optical axis in a focusing operation. Such a zoom lens system is of an inverted telephoto type because of the negative front lens group, and is a favorable format for designing a wide angle lens system.
Therefore, various designs of such zoom lens system have been provided. For example, U.S. Pat. No. 4,159,865 has disclosed a two group zoom lens system of an inverted telephoto type comprising a first negative lens group consisting of four or five lens components and a second positive lens group consisting of six or seven lens components. The second positive lens group is located at the image side of the first lens group with a variable air space formed between the first and second lens groups, said variable air space being varied during a zooming operation. However, since the zoom lens system disclosed in the U.S. patent requires ten or eleven lens components as described above, it is complex in construction, expensive, and has a considerable length along its optical axis.
To improve this type of lens system, the inventor of the present invention has suggested an inverted telephoto type two group zoom lens system consisting of six lens components in Japanese Laid-Open Patent No. SHO 54-114236. The first embodiment of the Japanese Patent has disclosed a two group zoom lens system comprising, from the object side to the image side, a first negative lens group consisting of a first negative component with a stronger image side surface concave to the image side, and a second positive component of a positive meniscus lens convex to the object side, and a second positive lens group consisting of third and fourth positive components, a fifth negative component and a sixth positive component.
The present invention relates to an improvement of the two group zoom lens system disclosed in the above-mentioned Japanese patent.